The present invention relates to the field of implanted medical devices (IMDs) and related data management. Specifically, the invention relates to network compatible RF wireless link or equivalent, configured to enable connectivity between various devices.
During the latter portion of the twentieth century, it became common to implant IMDs to provide therapy for a vast number of medical conditions. Such devices included electrical stimulation devices, pain control devices, and drug delivery systems. Additionally and as these devices became more complex, it became necessary to monitor both their operation and the patient""s condition.
At the same time, patients with IMDs have come to expect a fuller life post implant. These expectations include few, if any, restrictions on their lifestyle. Thus, it has become imperative that patients be allowed a great degree of mobility while their medical condition is being monitored and/or treated by the IMD. The traditional method of semi-annual or annual checkups for the IMD and the patient limits the frequency of monitoring. Moreover, the patient may feel that he must remain close to the physician""s clinic or the hospital where checkups take place. Further, emergency situations may sometimes occur which, in the mind of the elderly patient, demand very close proximity to the attending physician.
Moreover, advances in modern patient therapy and treatment have made it possible to implant a number of devices in a single patient. Successful management of the operation and assessment of the performance of each device in these patients may require monitoring these devices for periodic and frequent updates. Further, communication between the various IMDs in order to gain a complete medical history of the patient may be preferred so as to provide a coordinated clinical therapy. Going to the clinic for frequent checks may impose a considerable burden on the patient as well as an overall increase in the cost of health care. Accordingly, it is vital to have IMDs that are equipped with a communications system that connect to a link in such a manner that is transparent to the patient and yet provides the medical data required by the physician.
New developments in telehealth and telemedicine provide one avenue to address these issues. Telehealth is generally defined as the delivery of health care services from provider to patient via telecommunications links. Telemedicine, on the other hand, involves communications between health care providers and patients. Both of these technologies are intended to reduce the overall cost of medical care, as well as improving the access of patients to health care services. In the context of IMDs, developing systems that allow patients to be monitored remotely in the home require critical modular instrument technology as well as communications systems. This technology can help reduce the number of home visits and provide more time for the health care provider to respond to changes in the patient""s condition.
U.S. patent application Ser. No. 09/745,112, filed Dec. 20, 2000, xe2x80x9cInstrumentation and Software for Remote Monitoring and Programming of Implantable Medical Devices (IMDs)xe2x80x9d, incorporated by reference herein in its totality, describes a modular system that is adaptable to a variety of medical devices. The system includes communications technology to effect wireless transmission between various devices, patients, and health care providers.
As can be seen from the patents cited in the ""112 application, telemetry has been proposed as one of the communications systems. A system is taught in U.S. Pat. No. 5,113,869 that describes an implanted ambulatory ECG patient monitor with a longer range telemetry communication capability. One of the external devices disclosed in the ""869 patent is a wrist-worn alarm that emits an audible warning signal to alert the patient that the implanted ECG monitor has detected an arrhythmia. Another external device in the ""869 patent is a belt-worn xe2x80x9cfull disclosure recorderxe2x80x9d containing a high capacity memory for receiving and storing data telemetered from the implanted ECG monitor when its memory capacity is exhausted.
A similar method of communication for an implanted pacemaker-cardioverter-defibrillator device is disclosed in U.S. Pat. No. 5,336,245. The ""245 patent teaches how data accumulated in the limited capacity memory of the IMD is transferred to a larger capacity external data recorder. The accumulated data is then forwarded via a modem-equipped computer-based device to a clinic.
RF coupled systems are extensively employed communications systems in modern IMDs. In such systems, information is transferred from a transmitting coil to a receiving coil by way of a radio-frequency carrier signal. The carrier signal is modulated with the data that is transmitted through the use of an appropriate modulation scheme, such as phase shift keying (PSK), frequency shift keying (FSK), or pulse position modulation (PPM), among others. These systems, however, have been used primarily to achieve communications between an IMD and an external programmer. Issues related to this type of communication are disclosed in U.S. Pat. Nos. 5,683,432 and 5,843,139 issued to Goedeke, et al., both incorporated herein by reference in their totality.
Advances in the art have made it possible to monitor IMDs and the patient from just about anywhere in the world. Such a system is disclosed in U.S. Pat. No. 5,752,976 issued to Duffin et al., and incorporated herein by reference in its entirety. This system provides means for communicating with an IMD implanted in a mobile patient. The IMD includes a telemetry transceiver for communicating data to an external device either worn by the patient or located in close proximity to the patient. The communicated data is then transferred to a remote medical support network.
Implementation and operation of most, if not all, RF communication systems involves a balancing or compromising of certain countervailing considerations. These are associated with such interrelated operational parameters as data transmission rate and transmission range, among numerous others. For example, the adjustment of one operating parameter may permit or require the adjustment of one or more other operating parameters. At the same time, predetermined system performance goals and/or requirements must be met. Moreover, predetermined limitations imposed upon operational parameter adjustment must be adhered to. These conditions result in the trade-off between signal range and signal power. Simply stated, for a given communication scheme, a more powerful (e.g., higher amplitude) signal has a longer effective range. Thus, decreasing the range of a communication link (e.g., reducing the distance between transmitters and receivers in the link) allows the transmission power to be decreased, while other operational parameters, e.g., data transmission rate, can be held at a constant value.
Another example is the trade-off between data transmission rate and transmitted signal power. Those skilled in the art will appreciate that, in most instances, increasing the data transmission rate over an RF channel typically requires increased signal bandwidth. Increasing the bandwidth, in turn, tends to lead to increased power consumption by the communication system in order to maintain an acceptable signal-to-noise ratio.
Still another example of the trade-offs associated with the operational parameters, and system performance goals of an RF communication system is that associated with data transmission rate versus signal range. As noted above, increasing data transmission rate typically requires increasing the bandwidth of the transmitted signals. Conversely, decreasing data transmission rate typically allows for a reduction in the signal bandwidth. If bandwidth can be reduced, the range of operation will be increased for a given level of power consumption. The foregoing and other trade-offs associated with various operational parameters of a communication system arise in most applications involving RF transmission and reception. The nature of the interrelation between the various operational parameters may vary depending, for example, upon the type of modulation used (such as PPM, FSK, FM, AM), as well as upon the type of coding used.
In the context of IMD systems, there are additional considerations that must be addressed. Primary among these are reliability of transmission and reception, and conservation of the power of the IMD. Conservation of implanted device power, which, in most cases, implies minimizing current drain upon an implanted device""s internal battery in particular, renders the aforementioned trade-offs highly significant.
In one aspect, the present invention implements a method and apparatus for establishing a communications link between an IMD, a patient-worn transponder and a remote monitoring station while, at the same time, minimizing device current drain. Minimal current drain is achieved by scheduling periodic interrogation of the data collected by the IMDs and subsequent retransmission to a remote location. In addition, the IMD may also transmit unscheduled data when a significant event, such as a cardiac arrhythmia or device intervention, occurs.
A further aspect of the present invention provides a communications system that transmits data telemetered from the IMD to a patient-worn device. These data can then be transferred from the patient-worn device, equipped with a Bluetooth (BT) or Home RF (HRF) communication system, to a plurality of nodes similarly equipped with BT or HRF technology. Such wireless data transfer will culminate in the receipt of such data by a transceiver that sends the data to a remote information network and/or medical clinic.
In yet another aspect of the present invention, a telemetry transceiver within the IMD is implemented to communicate data to and from the IMD in an encrypted code. The IMD telemetry transceiver has a range extending outside the patient""s body sufficient to reach a patient-worn external device. This external device may be worn on the patient""s wrist in one embodiment, or as a neck worn pendant, a modified belt device, or pager-like device attached to the belt in other embodiments. The patient-worn device would have a BT or HRF chip and would re-transmit to a transceiver also equipped with BT or HRF technology, which is connected to a phone line, cellular phone, satellite communication methods, telemetry, or some other means to transmit the data. Accordingly, the patient may move freely around the home and/or yard and still be in communication with the remote network or medical clinic via this method.